The present invention relates to measurements of holding time in communication networks, for use in tools for management and planning of the network.
Traffic volume, call attempt number and holding time measurements are the basic measurements performed in telecommunication networks. These parameters provide the operators with invaluable information about the network status.
These measurements form the basis of capacity planning and element dimensioning of these networks.
Measurement methods and systems used today were designed for networks carrying predominantly voice traffic. In today""s networks the characteristics of the traffic have changed to that extent that some of the preconditions assumed has became obsolete. As a result of this some measurement results are incorrect. This poses a big problem because statistics based on these misleading results are used as basis for decisions about the future investments into the networks and operation and maintenance issues.
The above mentioned key parameters are measured in network elements using event counters. The measurements are performed in fixed time intervals. However there are performance parameters, which are not easy to measure directly.
One of these parameters is the holding time. Network elements today provide measurement results of the average holding time during the measurement interval, but in fact this value is calculated from the traffic and call attempt counter values for the given interval.
Another way to get these statistics is to process data in the charging databases. Some operators use traffic statistics from these databases, but this solution has several shortcomings. Data stored in the charging database are confidential and strategically sensitive. Also the processing of these large amounts of data is expensive and can not be performed continuously to have up to date statistics on a minute or even daily basis.
As it was mentioned previously the holding time parameter is calculated based on the traffic and call attempt counters. Basically the following formula is used:
Hi=Ai/Ii 
where:
Hi: is the holding time
Ai: is the traffic
Ii: is the call intensity (number of call attempts per time unit)
i: index of the measurement interval
For example lets assume a 30 minutes long measurement interval, 180 Erlang""s measured by the traffic counter and 3600 call attempts counted during this interval. Based on the above formula this gives us 90 seconds holding time, as the call intensity is 2 calls per second (3600 call attempts divided by the length of the measurement interval).
In the next example lets assume again 30 minutes long measurement interval and 180 Erlang""s traffic measured, but the call attempt counter value now is only 36. The above formula gives us in this case 9000 seconds holding time. How could we measure 9000 seconds holding time in 1800 seconds long measurement interval?
The problem with this value is that it is calculated based on the traffic and call attempt counters only from one measurement interval. The assumption that the traffic measured during a measurement interval is generated by the call attempts arriving during that interval is invalid. If we assume 36 call attempts generated at the beginning of the measurement interval and calls not terminated before the end of the interval the resulting traffic is 36 Erlang""s. This means that 36 call attempts can not generate more traffic than 36 Erlang""s during the measurement interval irrespective of the holding time.
The explanation of the above problem is that large portion of the measured traffic was generated by call attempts from the previous measurement intervals. The above formula is correct if the traffic generating process gets into a quasi stationary state in considerably shorter time than the length of the measurement interval.
Another practical problem is that in real life the traffic seems to change its characteristics so fast that it can not settle into a stationary state. This means that the above formula can not be used to obtain correct measurement results for example from links carrying traffic towards Internet service providers.
It is an object of the present invention to produce a method and arrangement for measuring holding time in a communication network which avoids the shortcomings of the traditional method. Using traffic volume and call attempt number measurements from earlier measurement intervals as well it is possible to calculate the holding time parameter of the calls generated during the current interval in a much more accurate way.
While the error of the traditional way of measuring holding time depends not only on the confidence of traffic and call attempt measurements but also on the characteristics of the holding time profile of the users, the method according to the present invention is affected mainly by the confidence of the traffic and call attempt measurements.
A further object of the invention is to produce a method and arrangement for measuring holding time that cope with fast changing characteristics of the traffic in a communication net.
Other objects of the invention are to implement the above-described method into performance management systems or any other systems or tools postprocessing measurement results from network elements.
The objects described above are achieved in a method, arrangement and various fields of use as described in the appended patent claims.